Any of the true strong acids are completely dissociated in solution. This means that they will completely form the ions, basically the same way they would if they are a salt. So HCl, HBr and HI (which are all strong acids) will form H+ and Cl-, H+ and Br-, and H+ and I- respectively. This is the definition of a strong acid. For weak acids, the more that they will dissociate into their ions in solution the stronger it will be. This is why weak acids with higher Ka are stronger acids, because they dissociate more.